Compounds of the following formula (I) are useful as selective herbicides to kill undesirable plant growth among crops such as cotton, soy beans, peas, corn, wheat and rice: ##STR5## wherein R.sup.1 is an alkyl group of 1 to 12 carbons, as disclosed in European Patent Application No. 79300098.5 published Aug. 8, 1979 as publication No. 3416. The compounds of formula (I) are useful both as pre- and post-emergence herbicides when applied at a rate of 0.1 to 5.0 kilograms per hectare.
Processes for the synthesis of compounds of formula (I) are known as seen by a reading of European Patent publication No. 3416. However, many of such processes are disadvantageous from a commercial standpoint in view of the need for nitrating a compound of a formula such as: ##STR6##
It is an object of the present invention to provide a process for the preparation of compounds of the formula (I) using 2-amino-5-hydroxybenzoic acid or, considering steps leading to 2-amino-5-hydroxybenzoic acid, ortho-nitrobenzoic acid as the starting material. The process of the invention has the advantage of utilizing a starting material with a nitrogen in place at the desired position for the nitro group of the compounds of formula (I). The method of the invention thus is in contrast to known or obvious methods for the synthesis of compounds of formula (I) which require nitrogen substitution on the ring as one of the final steps. This introduction in the prior art of a nitrogen atom on an aromatic ring may be disadvantageous in view of nitrogen atom additions at other than the desired position para to the phenoxy substituent.